Japanese Patent Laying-Open No. 2001-8380 discloses a power management system allowing transmission of electric power between a house and a battery of an electric vehicle. The system includes reserved power amount determining means for calculating an amount of power to be reserved in the battery to enable normal use of the electric vehicle, and a controller for restricting the amount of power supplied from the battery to the amount obtained by subtracting the reserved power amount from the remaining capacity of the battery.
According to the power management system, the amount of power that allows normal use of the electric power is reserved in the battery and the remaining power of the electric power is supplied to the house. Therefore, in case of emergency or the like, the electric vehicle can be used.
In the power management system disclosed in Japanese Patent Laying-Open No. 2001-8380, while an electric vehicle is used as a source of power for the house, state of power demand and supply in the house is not considered when the electric power is supplied from the electric vehicle to the house or when the electric vehicle is charged from the house.